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Durandal: Quick Start

Durandal is a lightweight JavaScript framework designed to make building Single Page Applications (SPAs) simple and elegant. It has strong support for MVC, MVP and MVVM so that no matter what type of front end architecture you prefer, Durandal can handle the task.

With RequireJS as its base and a thin layer of conventions, Durandal can provide amazing productivity while helping you to maintain SOLID coding practices. Pair that with out-of-the-box support for rich UI composition, modal dialogs, eventing/messaging, widgets, transitions, routing and more....and there's no doubt you'll be able to build whatever apps you can imagine.

While Durandal has only been publicly available for about a year now, the community has grown at a breakneck pace.

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As a result, we’ve launched a Kickstarter to help us accomplish some amazing things in 2014. We hope you’ll check it out. But now, I’d like to show you how to build a simple Durandal application yourself.

There are several ways to get started with Durandal, depending on your platform choice. While Durandal is a pure JavaScript library, independent of any server-side platforms, we try to package it up in a variety of ways that are appealing to web developers. For this brief tutorial, we’ll use our raw HTML Starter Kit. You can download that directly from the official site’s downloads page.

Once you’ve downloaded the HTML Starter Kit and unzipped it, you can actually run the sample app immediately by opening the index.html file in Firefox*, or by spinning up a web server and browsing to the index page.

The starter kit application demonstrates a basic navigation architecture with routing, history, data-binding, modal dialogs and more. But, we’re not going to look at that just yet. Instead, we’re going to write our own little app from scratch. To do this, locate the app folder and delete its contents, then delete the index.html. Now we have a completely blank project, pre-configured with all our scripts and css.

*Note: IE, Chrome and Safari don't like serving the files directly from the file system. If you would like to use one of these browsers, simply use your preferred web server technology to serve the files.

All we have here are a few css files, a single div called “applicationHost” and a single script tag. We’ve added Bootstrap and FontAwesome here so we can easily make things look decent, but they aren’t required by Durandal. The important piece to notice is the script tag.

Durandal encourages modular code practices by using RequireJS as one of its core building blocks. In a Durandal app, all JS code is written in modules. The script tag in our index.html loads RequireJS which facilitates the framework’s module strategy. Once the module loader is initialized it then uses the data-main attribute to start up our app. This attribute points to our main module. This is much like the main function in most c-based languages. It is the entry point for our application. Let’s go ahead and create that module now. To do that, first create a file named main.js and place it in the app folder. Here’s the code for that file:

This is pretty standard “boilerplate” configuration for most Durandal apps. But, let’s go over this piece by piece:

At the top we have the requirejs.config block. This section configures the module system so that it can find our core libraries. It’s just a set of relative paths, so that the first time we reference “jQuery” for example, the module system knows where to load it from. Here you see that we have paths configured for the requirejs text plugin (used to load views), Durandal’s core modules, Knockout and jQuery. In the same way that Durandal uses RequireJS for modules, it uses Knockout for data-binding and jQuery as its browser abstraction.

After we set up the RequireJS configuration, we define our main module. All code in Durandal is written in modules and takes the following form:

To create a module you call the define function. You pass a function to define which serves as a factory for your module. Whatever you return from this function becomes your module instance. You can return an object to create singleton object modules or a function to create class constructor modules. Additionally, you can declaratively express dependencies upon other modules. To import another module into your module you use the require function.

In our main module above, you can see that we import or require two of Durandal’s modules: system and app. We then use the system module to turn on framework debugging. After that we use the app module to set our app’s title and load two optional plugins. Finally, we tell the app to start, which is an asynchronous action, and when that completes we call a curious function: setRoot.

The call to setRoot is what actually causes something to be rendered on the screen. You can think of the root as your “main window”, “master layout” or the “shell” of your application. The parameter points to the module which contains our shell’s behavior. The only problem is..that doesn’t exist yet. So, let’s create it.

The Shell

Most components in Durandal contain both “behavior” and “presentation”. Your application’s shell should be no exception to this rule. We’ll represent these two different concerns by creating two files: a JavaScript file for the behavior and an HTML file for the presentation. Under your app folder create: shell.js and shell.html. I’ll give you the code for each of those now, then we’ll see how it all works.

Notice that our shell.js defines a module as we have previously discussed. It has dependencies on two other modules: app and knockout. Our module returns an object literal as its definition. This object has one property, name, and one function, sayHello. The name property is special. Here, we have used Knockout to create an observable property. An observable property supports two-way data-binding to html, change notification and a number of other features. Notice that the sayHello function uses this property to display a message box with Durandal’s app module.

To fully understand this code, you need to look at it side-by-side with the HTML. Notice how the HTML has data-bind attributes in it. These attributes declaratively connect the HTML to the properties and functions in the module we just looked at. See how the input tag has a data-bind attribute that connections its value to our name property? It also specifies that our property should be updated after key down events (as opposed to focus change, which is the default). Also, take a look at the button. Its click event is bound to our sayHello function. Furthermore, the button will only be enabled when the name property has a truthy value. Pretty cool! Go ahead and run the app by opening index.html in Firefox or spinning up a web server to view it in another browser. When you do this, here’s what’s going to happen:

RequireJS will load.

RequireJS will load your main.js and configure the framework.

Your main.js will present the app by calling setRoot.

The shell.js and shell.html files will be loaded, data-bound to one another and injected into the applicationHost div in the page.

Once it’s loaded, try typing in the input field and notice how the button’s enabled state changes. Then, click the button to see what happens.

Navigation

This is all pretty cool, but most applications don’t just have one page. So, let’s turn our shell into a navigation app. To start, rename your shell.js to home.js and your shell.html to home.html. Now, create two new files which will serve as our navigation shell. Here’s the source for the new shell.js and shell.html.

Looking at our navigation shell, you can see the same module pattern. Here we are requiring our router plugin and using that to create an object. We configure the router with a single route that points to our home module. This router configuration specifies the route pattern to match on, the title to display, the moduleId to load when the route is matched and whether or not we should tag this route as part of our visible navigation (nav:true). After we configure our routes, we then call buildNavigationModel which takes the route info, and builds a special collection that we can data-bind to for display as a top-level navigation UI. Finally, we activate the router. All of this takes place inside a function called activate. Every time Durandal presents a component on screen, it will look for an optional activate callback. If present, it will invoke it prior to data-binding. This allows modules to execute custom activation code, such as configuring the application’s router in this case.

Once again, it’s easiest to understand if you look at the module side-by-side with it’s view. If you do that, you will first see how we are data-binding to the navigationModel property in order to generate a navbar. Each navigable route is turned into an li with a link that is bound to the route’s hash and title. As part of the navbar, we also bind an animating spinner icon to the router’s isNavigating property. As a result, whenever we are in the process of navigating from one page to another, the spinner will be visible and animating.

At the bottom of the view is a special router binding which connects to our router in the module. This serves as a placeholder where the current “page” will be displayed. The transition property indicates that whenever the page changes, Durandal should use the “entrance” transition animation.

Go ahead and run it again. It looks pretty similar to before, except now there’s a navbar. It’s not very impressive because we still only have one page. Let’s create a second page so we can navigate back and forth.

Mount Rainier

Let’s create a second page that calls Flickr and gets back a bunch of pictures to display of Mount Rainier. Our first step is to add another route. Update your shell’s router config so that it has these two routes now:

I bet you can figure out how this works. Our module uses the http plugin to call the Flickr api in its activate callback. It then stores that data in it’s images observable array property. The view simply binds to that array of data.

If you run the app now, you’ll see two items in the navbar and you’ll be able to navigate back and forth between them. You can also use the browser’s back button. There’s lots more details and tons more that Durandal can do. At this point, you might want to download the original starter kit and take a look at it in more detail to see a few more interesting tidbits. You’ll probably also want to download the official samples to see how other features work, like pub/sub messaging, custom modal dialogs, widgets, advanced view composition and more. If you want to see something really cool, check out the app we’ll build as part of our Kickstarter funded training series.

Durandal makes building rich, dynamic JavaScript apps simple by encouraging a modular approach. It’s no surprise that our community is growing so fast. We’re only getting started with our plans and we hope you’ll consider joining us on the adventure. Please have a look at our Kickstarter. We’ve got some cool goals for the 2014 year...and some awesome rewards for you. The web is changing, and it’s looking like a bright future is in store. We hope to see you there!

About the Author

Rob Eisenberg is a JavaScript expert and .NET architect working out of Tallahassee, FL and he is the President of Blue Spire Consulting. Rob got his start with computer programming at the age of nine, when he thoroughly fell in love with his family's new Commodore 64. His fascination with programming started with the Commodore Basic language, then moved to Q Basic and QuickBasic and quickly continued on to C, C++, C# and JavaScript. Rob publishes technical articles regularly at devlicio.us and has spoken at regional events and to companies concerning Web and .NET technologies, Agile software practices and UI engineering. He is coauthor of Sam's Teach Yourself WPF in 24 Hours and is the architect and lead developer of the Durandal and Caliburn.Micro frameworks.